1. Field of the Invention
The disclosure relates generally to the field of magnetic disk drives, and more particularly to apparatus and methods related to testing disk drive components.
2. Description of the Prior Art
Magnetic disk drives are used to store and retrieve data for digital electronic apparatuses such as computers. A typical magnetic disk drive comprises a head, including a slider and a transducer, in very close proximity to a surface of a rotatable magnetic disk. The transducer, in turn, includes a write element and/or a read element. As the magnetic disk rotates beneath the head, a very thin air bearing is formed between the surface of the magnetic disk and an air bearing surface of the slider. The air bearing causes the head to “fly” above the surface of the magnetic disk with a separation (“fly height”) that is typically less than 40 nanometers in contemporary disk drives. As the head flies over the magnetic disk, the write element and the read element can be alternately employed to write and read data bits along a magnetic “track” on the magnetic disk.
It will be appreciated that the head is a highly complex component and, accordingly, heads are preferably qualified before being assembled into disk drives. Commonly, heads are tested after being assembled into either a Head Gimbal Assembly (HGA) or after one or more HGAs are assembled into a Head Stack Assembly (HSA). The HGA typically comprises the head, a load beam, a gimbal that attaches the head to the load beam, a swage mount, and electrical traces to facilitate electrical connection of the transducer of the head to a pre-amplifier circuit. The HSA comprises one or more HGAs in a stacked arrangement for use with one or both sides of a magnetic disk and/or multiple magnetic disks. The HSA also typically comprises an actuator arm structure that can pivot in response to torques applied by a voice coil motor.
A spin stand is a common testing apparatus for testing writing and reading characteristics of heads. Generally, the spin-stand includes a rotatable disk and a positioning device that secures a HGA or HSA. The positioning device allows the head to be moved to a desired position over the disk. Accordingly, the positioning device typically includes two coarse motors for moving the head in two orthogonal directions relative to the disk.
One issue with spin stand testing relates to the problem of keeping the head aligned with a track on the disk. In a disk drive, a feedback loop known as a closed-loop servo is employed to keep the head properly aligned. The closed-loop servo relies on regularly spaced patterns on the disk, known as servo bursts, to determine any misalignment, and then corrects for the misalignment by adjusting the position of the head. However, spin stands historically have been “open-loop” systems, meaning that there is no feedback mechanism for keeping the head aligned with a track. Open-loop systems designed to have very high mechanical precision worked adequately when tracks were relatively wide. However, the demand for increased information storage density and associated improvements in write and read elements have lead to narrower track widths and narrower read elements, and therefore, what were once considered to be very small sources of mechanical imprecision now can cause the head to move significantly off-track during testing.
Accordingly, what is needed is a spin stand that is able to dynamically adjust the position of the head to keep the head aligned with a track during testing.